Straining apparatus for paint and the like



April 16, 1968 G. N. TIPPING 3,378,143

STRAINING APPARATUS FOR PAINT AND THE LIKE Filed March 5, 1967 5 SheetsSheet 1 I I w m INVENTOR.

GEOFFREY NEVILLE TIPPING BY fizz 1% M W AGENTS G. N. TIPPING STRAINING APPARATUS FOR PAINT AND THE LIKE April 16, 1968 5 Sheets-Sheet 2 Filed March 5,

A: z z 7 m 4 A l A m FIGZ INVENTOR. GEOFFREY NEVILLE TIPPING AGENTS April 16, 1968 G. N. TlPPlNG A STRAINING APPARATUS FOR PAINT AND THE LIKE 3 SheetsSheet 5 Filed March 5, 1967 FIG-.3

c a: o ooo ooooocooo oooco INVENTOR. GEOFFREY NEVILLE TIPPING BY M AGENTS United States Patent 3,378,143 fiTRAlNING APPARATUS FUR PAINT AND THE LIKE Geoffrey Neville Tipping, Waterlooville, Hampshire, England, assignor to Jenag Equipment Limited, Waterlooville, Hampshire, England Filed Mar. 3, 1967, Ser. No. 626,363 Claims priority, application Belgium, Mar. 11, 1966, 677,750 7 Claims. (til. 210-411) ABSTRACT OF THE DISCLGSURE Paint and the like is fed to the flat filter element of a paint strainer by a positive displacement pump synchronously driven with another positive displacement pump which withdraws filtered liquid from the element and partly returns the liquid under pressure to a wiper arm on the discharge side of the element and resiliently held close to the element. Orifices in the arm discharge the liquid against the element whereby accumulated solids are dislodged from the face of the feed side of the element, and clogging of the element is prevented. Certain dimensional relationships are important for successful operation.

Background of the invention This invention relates to strainers for paint and the like.

It has previously been proposed to strain paint and similar dispersions of fine solid particles through a filter medium from which the accumulating cake of coarse particles is dislodged periodically by filtered liquid directed toward the discharge face of the medium from an orifice which scans the face.

Such devices have been disclosed in US. Patents 2,204,-

349 and 2,338,417 to 2,338,419, also in British Patent No. 495,112. Although their principle of operation appears to offer a solution to a long-standing problem of the paint and ink industries and of related fields, they have not found wide practical application. The known devices require constant surveillance and careful maintenance. Breakdown by wear and mechanical failure is relatively frequent.

It has now been found that the shortcomings of the known devices can be overcome, and that paints, inks, and simiiar viscous liquids carrying finely divided solids other than the impurities to be removed may be strained successfully in continuous operation in devices based on the same operating principle, but embodying certain improvements.

Summary of the invention The strainer of the invention differs from the known devices by the provision of a pressure pump connected to the feed compartment of a chamber divided by a filter element. The pump is operated in synchronization with another pump which is connected to the discharge compartment of the aforementioned chamber and supplies back flushing liquid in a manner known in itself. The pump arrangement permits the entire apparatus to be operated under positive pressure, thereby eliminating the difficulties resulting from aspiration of air.

A wiper member is rotatably mounted in the discharge compartment in such a manner that an orifice therein is directed toward a face of the filter element and sweeps the face of the plate-shaped filter element with a stream of back-flushing liquid during its rotation. The wiper member is axially movable in the chamber and is urged toward the filter element by resilient means, thus avoiding seizing of the wiper member if the filter element is deformed by the filtering pressure.

3,378,143 Patented Apr. 16, 1968 Because of the axially resilient mounting of the wiper member, a precisely selected clearance can be maintained between the wiper member and the filter element at all times, thereby greatly increasing the useful life of both. The eificiency of the back flushing operation depends greatly on the dimensional relationship between this clearance and the size of the perforations in the filter element, if a filter element having spaced perforations is employed.

Other features and many of the attendant advantages of this invention will readily become apparent from the following detailed description of a preferred embodiment when considered in connection with the accompanying drawing.

Brief description of the drawing In the drawing:

FIG. 1 shows a paint strainer arrangement of the invention in side elevation;

FIG. 2 illustrates the strainer portion. of the apparatus of FIG. 1 in elevational section; and

FIG. 3 shows the device of FIG. 2 in fragmentary front elevation, parts of the structure being broken away to reveal internal details.

Description of the preferred embodiment Referring now to the drawing in detail, and initially to FIG. 1, there is shown a strainer chamber 1 of fiat, cylindrical cup shape closed by a flat circular cover ll. As better seen in FIG. 2, the chamber 1 is axially divided into a feed compartment 2 and a discharge compartment 3 by a plate-shaped filter element 4 assembled from a filter medium 40, such as canvas, and two perforated supporting metal discs 41), in on either side of the canvas. A normally plugged filling nipple 5 gives access to the top of the feed compartment 2, and a feed conduit 6 has an orifice near the bottom of the compartment 2.

A discharge conduit 7 communicates: with the bottom of the discharge compartment 3 which also encloses a wiper arm 8 mounted on a hollow shaft 9 coaxial with the chamber 1. The shaft 9 is journaled in the chamber 1 by means of a pressure packing 10. As is better seen in FIG. 3, the wiper arm 8 extends along a diameter of the compartment 2 and is provided with radially elongated slots or orifices 11, connected to the bore of the shaft 9 by the hollow interior of the arm 8.

A wide outlet conduit 12 at the bottom of the feed compartment 2 is normally closed by a sludge valve 13. The conduit '7 connects the compartment 3 with the suction inlet of a positive-displacement gear pump 14 whose discharge conduit 15 is provided with a throttle valve 15 and a normally closed drain valve 19. A back-flushing conduit 17 connects the discharge conduit 15 with the bore of the hollow shaft 9 and is provided with a control valve 1.6a. The pressure in the discharge conduit 15 may be read from a gage 18.

The feed compartment 2 is equipped with a valved air Vent 24. The positive or negative pressure within the dis charge compartment 3 is indicated on a compound gage 25 mounted in a threaded bore 26 of the chamber 1.

Liquid to be filtered is fed to the conduit 6 by a positivedisplacement gear pump 20 which is connected to the pump 14 by a common drive consisting of an electric motor 21 and a reducing gear transmission 22. The pump 20 has a smaller capacity than the pump 14. A drive chain 23 engaging a sprocket 31 on the output shaft of the transmission 22 drives the wiper arm 8.

As is best seen in FIG. 2 the shaft 9 carries a fixedly fastened sprocket 31' driven by the chain 23. The chamber 1 has a fixed flange 27 in which the shaft 9 is coaxially rotatably received. A loose flange 27 is secured to the fixed flange 27 by three bolts 28 which slidabiy pass through openings in the flange 2'7. Helical compression raw;

springs 29 on the bolts 28 the flange a! toward the fixed flange 27. The 27 axially abuts against a collar 30 on the shaft Q and thereby urges the shaft and the wiper arm 8 inward of the chamber 1 and toward t 1c filter assembly 4.

The afore-described apparatus operates as follows:

Assuming the filter arrangement ori ally to be empty, the nipple 5 is opened and the apparatus is filled with liquid medium compatible with the material which it is intended to strain. Air may escape through the temporarily opened vent 24. The chamber 3. is then sealed by plugging the nipple 5, the suction inlet of the pump 29 is connected to a container holding the material to be strained, and the motor 21 is started.

A slurry is fed to the compartment 2 by the pump 2! while a greater volume of liquid is withdrawn frcm the compartment 3, by the pump 14 and partly returned from the outlet of the pump to the compartment 3 throu h the back flushing conduit 17. The valve 15 is to n e the volume of liquid discharged from the valve 15 equal to the volume or" the material fed to the compartment 2.

his conidtion is reached when the reading of the gage is stable. The valves 16, 1621 are set in such a manner that the reading of gage 25 is posilive at all times, that is, the pressure in the discharge compartment 3 is highJr than atmospheric pressure at all times, and is maintained by the pump 2%).

As solids are deposited on the face of the filter assembly 4 in the feed compartment 2, the pressure reading on the gage 25 tends to drop, and adjustment of the valves 16, 16a may be necessary during an initial period of operation until a steady state is reached.

The wiper arm 8 sweeps the face of the supporting disc 4b with a small clearance maintained by projecting integral spacer portions 8' of the arm and by the springs 29 to provide a restricted passage from the orifices ill to the discharg compartment 3 regardless of deformation of the filter assembly 4 under the pressure differential in the compartments 2, 3. A clearance between the arm 8 and the supporting disc 4b not substantially greater and preferably smaller, than the average cross sectional width of the aligned perforations in the discs 40, 4b which form continuous axial channels through the filter assembly 4 has been found to be essential to continuous troublefree operation of the strainer.

The stream of liquid directed from the slots 11 toward the perforations loses much of its kinetic energy by turbulence if this clearance is not maintained, whereby the solids deposited on the disc and the medium 4a are not effectively dislodged. The useful life of the arm 8 and of th filter assembly is shortened if the arm is in continuous contact with the filter assembly at all times, and the strainer may sutfer serious damage if the arm cannot yield in an axial dir ction as required by the unavoidable deformation of the filter assembly 4.

The spacing of the perforations in the filter element 4 and the dimensional relationships between the slots or orifices 11 and the perforations having an important hearing on the efiiciency of the back flushing operation. It has been found that the illustrated shapes and dimensions of the orifices and of the perforations must be adhered to if the thickness of the solid cake or layer on the face of the filter element 4 in the feed chamber 2 is to be held to a minimum. More specifically, the orifices 11 should be radially elongated and increase in width in a radially outward direction. Its length should be much greater than the approximately uniform spacing of the perforation in the major portion of the filter element whose face is being swept by the orifice during rotation of the arm 8.

When a heavy buildup of solids on the filter assembly is prevented by back flushing, the actual pressure differential between the compartments 2 and 3 can be made very small, not significantly greater than is needed to maintain the desired rate of liquid flow through the perforated plates 4b, 4c and the filtering medium 4a in the ELL absence of a deposit. The solids, therefore, are not firmly held to the filter assembly. and most of the solids float freely in the feed compartment 2, and settle by gravity. When a suificient amount of solids accumulates in the outlet conduit 12, the valve T31 is briefly opened to release them, and the resulting temporary imbalance in the compartments of the cham er 1 is compensated for by suit able manipulation of the valves 16, 1611 as described above. The setting of these valves is not changed otherwise during operation of the apparatus during a full working day. The inherent synchronization of the pumps 14, 2d is essential to continuous operation requiring little or no attention on the part of an operator.

Because every portion of the apparatus is under posie tive pressure at all times, air is not aspirated through seals or packings. The valved vent 24 is opened only during the initial charging of the apparatus with liquid. The apparatus may be drained through the valve Ifi at the end of a run while the vent 24 is open. The cover 1 may be released from the chamber 1 in a conventional manner, not illustrated, for cleaning the interior of the chamber and for changing the filter medium. The filter ssembly 4 is releasably fastened to the shell of the chamber 1 in a manner not shown, and is normally held in its illustrated position by the pressure differential of the compartments 2, 3.

The illustrated and described strainer has been found effective in the removal of coarse particles and particulate contaminants from paints and printing inks which are dispersions of finely divided pigments and resinous material in organic solvents or water. The filter medium is chosen to pass the pigment particles, but to retain coarser particles including agglomerations of pigment particles. Other applications for the illustrated apparatus will readily suggest themselves to those skilled in the art, and may call for minor modifications.

It should be understood, therefore, that the foregoing disclosure relates only to a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

1. In a strainer arrangement, in combination:

(a) a substantially closed chamber;

(b) a plate-shaped filter element dividing said chamher into a feed compartment and a discharge compartment, said filter element having a face in said discharge compartment;

(c) means for maintaining a pressure higher than atmospheric pressure in said compartments during operation of said arrangement including a first pressure pump connected to said feed compartment, said filter element being permeable to liquid;

(d) a second pressure pump having an inlet connected to said discharge compartment for withdrawing said liquid from the same, and having an outlet;

(e) a wiper member mounted in said discharge compartment for rotation about an axis and for axial movement toward and away from said face of the filter element;

(f) yieldably resilient means urging said wiper member toward said face during said rotation, said wiper member being formed with an orifice directed toward said face;

(g) a back flushing conduit connecting said outlet of the second pump with said orifice for discharge of said liquid from said orifice under the pressure of said second pump;

(h) valve means communicating with said back flushing conduit for releasing an adjustably throttled stream of said liquid from said conduit;

(i) first drive means connected to said pumps for operating the same in synchronization; and

(j) second drive means for rotating said wiper member about said axis during operation of said pumps.

2. In an arrangement as set forth in claim 1, clearance means for maintaining a predetermined clearance between said orifice and said face against the restraint of said yiel-dably resilient means and for thereby providing a restricted passage between said orifice and said discharge compartment While said pumps are being operated.

3. In an arrangement as set forth in claim 2, said filter element being formed with perforations through said face, said clearance being not substantially greater than the average cross sectional Width of said perforations.

4. In an arrangement as set forth in claim 3, said clearance being smaller than said width.

5. In an arrangement as set forth in claim 1, said pumps being positive displacement pumps.

6. In an arrangement as set forth in claim 1, said wiper member being elongated transversely of said axis, 20

and said orifice being elongated in a radial direction relative to said axis.

7. In an arrangement as set forth in claim 6, said References Cited UNITED STATES PATENTS 1,452,151 4/1923 Genter et al 210-333 X 2,066,479 1/1937 Maclsaac 210414 X 2,310,587 2/1943 Ma-cNeill 210-411 2,909,286 10/1959 Norell 210-408 FOREIGN PATENTS 1,327,647 4/1963 France.

609,248 9/ 1948 Great Britain.

REUBEN FRIEDMAN, Primary Examiner.

I. L. DE CESARE, Assistant Examiner. 

